When the US highway system was inaugurated in late 1926, the only US route to initially serve San Angelo was US 385 (that is, the original US 385, not the current US 385). The new designation was added to Texas State Highway 9:
One of the many interesting things about this segment of US 34 is that it essentially follows the valley of the Colorado River between its headwaters in Rocky Mountain National Park and its confluence with the Fraser River in Granby. Consequently US 34 also provides access to all of the major water collection components of the Colorado-Big Thompson Project. Those include Grand Lake (Colorado's largest and deepest natural lake) and three artificial impoundments (Shadow Mountain Lake, Lake Granby, and Willow Creek Reservoir). Since there are many examples of highways which were originally built parallel to rivers, but which later had to be realigned because of water storage projects that were built in those valleys, I set out to explore whether US 34 had any historic alignments that existed prior to the reservoirs in the Middle Park area.
Of the "main" US highways (i.e. the one- and two-digit routes), the longest nine were all east-west routes (6, 20, 50, 30, 40, 60, 70, 80, 12). And if we take the longest 16 highways, only one of them is a north-south route (US 1, shown in red here):
That stands to reason, because the United States is roughly twice as wide from east to west as it is from north to south. So it makes sense that there would be more long east-west routes.